In earth boring and excavating for wells, deep foundations, tunnels and other geotechnical applications, fluids or muds have been used to hold open and maintain the stability of boreholes and excavations. These fluids or muds have used hydrostatic pressure and controlled interaction with the earth to accomplish their functions. The excavations have been kept full of the fluids or muds during the excavating or boring process, with or without circulation of the fluids.
Separately, in processes for improving the cohesion and load-bearing properties of granular or unconsolidated soils and other unstable granular earth formations or materials, reactive compositions have been injected into and mixed with the soils to cause solidification or hardening of the soils. These reactive compositions have comprised silicates cementitious grouts and other materials. The application of these soil-improvement materials and techniques has been done as a prelude to excavating, drilling, tunneling, or pile-driving, in order to render the soils resistant enough to support deep excavations for things such as foundation systems such as bored piles, or to bear the weight of structures erected on pad-type foundations or spread footings. These processes whereby weak soils are prepared to receive excavations for things such as foundation systems or other geoconstruction elements are generally referred to as ground improvement.
In a typical sequence of events for the construction of structures on poor soil, ground improvement techniques are used, followed by excavating or drilling to create deep foundation elements such as diaphragm wall panels, barrettes, or bored piles. Frequently the excavations or borings are made with the help of a fluid or mud as described above. In this two-step process the weak soil is first strengthened by ground improvement techniques such as reactive silicate injection or mixing, then excavations are created in or through the strengthened soil with the help of an excavating fluid or drilling mud. Finally, reinforced concrete is formed in the excavations in order to create a competent deep construction system.
In the prior art, silicates and silicate-reactive compounds have been injected into or mixed with granular, rubbleized or vugular earth formations, fills or other materials in advance of or during pauses in drilling or excavating, to strengthen or solidify the earth formations. Polymer-based fluids have been used for excavating and drilling, to support the walls of the excavations or wells. And silicates have been added to drilling muds in attempts to prevent heaving of shales. What is unknown in the prior art is the formulation and effective application of a single fluid which is both and at the same time a drilling mud or earth support fluid and a reactive, soil-permeating, silicate-based chemical-grouting ground-improvement or ground-solidification agent which is effective in the presence of unstable earth environments (e.g. sand).
As a result of the above, there remains and exists an unmet need for fluids that stabilize and/or make possible the excavation in the earth. The instant invention offers an improvement over the prior arts for both the stabilization of boreholes, earth excavations and the like; and ground improvement. An adaptation of the invention is useful during the preparation of guide-walls for diaphragm walls and the solidification of near-surface zones of loose soil.